We will continue to characterize temperature-sensitive mutants of polyoma virus that are defective in gene functions affecting cell growth regulation. In particular, we will search for mutants that are defective in the viral function required for induction of cellular DNA synthesis in resting cells. We plan to study the patterns of transcription of virus-specific RNA in cells showing a temperature-dependent transformed phenotype and to characterize the virus-specific RNA made in cells lytically infected with mutants blocked in early functions. We will continue to try to identify virion proteins that may be altered in various t.s. mutants.